Field of the Invention
The present invention relates to a gas supply manifold to be used as a constitutional element of a gas combustion device for a water heating apparatus and a production method of the gas supply manifold.
Description of the Related Art
A gas combustion apparatus of a water heating apparatus is generally configured to supply fuel gas from a gas supply manifold into a plurality of burner heads, i.e. combustion pipes. A gas supply manifold is disclosed in, for example, Patent Literatures 1 and 2.
A gas supply manifold disclosed in Patent Literatures has a nozzle forming member having a plurality of gas injection nozzles and has a cover member, the cover member being overlapped on the nozzle forming member, thereby constituting a gas supply path between the cover member and the nozzle forming member, both members being caulked and fastened. In such a caulking-fastening structure, a convex portion provided for one of the nozzle forming member and the cover member is inserted into a hole provided for the other member. In addition, a tip end portion of the convex portion is pressed so as to have a larger diameter than the hole. Thereby, the tip end portion of the convex portion is formed with an engagement portion which is engaged with a peripheral edge portion of the hole.
In such a structure, screw members are not required or such necessity is reduced unlike the case in which the nozzle forming member and the cover member are fastened with screws. Therefore, a gas supply manifold is produced at a low cost.
However, there is still a room for improvement in the related art as mentioned below.
In the caulking-fastening structure in the above related art, the tip end portion of the convex portion is only compressed and deformed to enlarge the outer diameter so as to form the engagement portion. Therefore, when the amount of compression and deformation of the convex portion is increased in order to enlarge the outer diameter of the engagement portion, the entire thickness of the engagement portion becomes thin, thereby reducing the strength of the engagement portion and strength of caulking-fastening. On the other hand, when the amount of compression and deformation of the convex portion reduces in order to increase the thickness of the engagement portion, the outer diameter of the engagement portion becomes small, thereby reducing the engagement area of the engagement portion and the peripheral edge portion of the hole and reducing the strength of caulking-fastening. Accordingly, in the related art, it has been difficult to caulk and fasten the nozzle forming member and the cover member in an appropriate condition, so that there is a room for improving the productivity.
On the other hand, the nozzle forming member and the cover member are constituted with relatively thin plate members. The gas supply manifold is generally provided with a plurality of valves to control an on-off and a flow rate of gas supply. In view of facilitating attachment of a plurality of valves and provision of the gas supply path communicating with the valves, one of the nozzle forming member and the cover member can be a die-cast product with a relatively large thickness. If such a measure is applied, the plate member is sometimes required to be fastened to an area of a base member with a large thickness.
However, in the caulking-fastening structure of the above mentioned related art, in order to appropriately form the engagement portion, the tip end portion of the convex portion is required to project out of the hole when the convex portion is inserted through the hole. When one of the nozzle forming member and the cover member is a die-cast product and has a large thickness and the hole is deep, it is difficult to appropriately fasten both members by the above-mentioned caulking-fastening structure. As a result, screws are inevitably used for fastening the nozzle forming member and the cover member. In such a case, the members for screwing require further cost and a screwing operation is complicated, thereby deteriorating the productivity and increasing the production cost of the gas supply manifold.